Carbon dioxide sequestration materials and processes

ABSTRACT

The disclosure provides methods and systems for sequestering and/or reducing carbon dioxide present in an industrial effluent fluid stream containing carbon dioxide. A scrubbing material comprising a first component, a second component (distinct from the first component), and preferably water, is contacted with the effluent fluid stream. The first component comprises a source of calcium oxide and a source of alkali metal ions. The second component comprises a slag having one or more reactive silicate compounds. Methods of reducing carbon dioxide from exhaust generated by combustion sources, lime and/or cement kilns, iron and/or steel furnaces, and the like are provided. Carbon dioxide emission abatement systems are also disclosed. Methods of recycling industrial byproducts are further provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/025,905 filed on Feb. 11, 2011, which issued as U.S. Pat. No.8,105,558, and which is a continuation of U.S. patent application Ser.No. 12/224,863 filed on Apr. 22, 2009, which issued as U.S. Pat. No.7,906,086, and which is a 371 U.S. National Stage of InternationalApplication No. PCT/US2007/005976 filed on Mar. 8, 2007, that claims thebenefit of U.S. Provisional Application No. 60/782,325 filed on Mar. 10,2006. The entire disclosures of each of the above applications areincorporated herein by reference.

FIELD

The present disclosure relates to emissions abatement processes and inparticular, to processes that sequester carbon dioxide from carbondioxide containing fluid streams.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Global climate change (i.e., global warming) is believed to be caused byanthropogenic emissions of greenhouse gases. Modeling of global warmingeffects predicts global increases in temperature and sea levels, shiftsin weather patterns, and more extreme weather events, including floodingand droughts. Greenhouse gases include carbon dioxide, methane, nitrousoxide, water vapor, ozone, and perfluorocarbons/chlorofluorocarbons. Ithas been estimated that carbon dioxide accounted for about 84% ofgreenhouse gas emissions in the United States in 2000. The rate ofemissions of carbon dioxide (CO₂) and other hazardous air pollutants ishighly correlated to both economic and industrial growth and hasincreased significantly since the mid-1800s. CO₂ is typically generatedby combustion of hydrocarbons, fossil fuels and/or by various industrialprocesses that generate carbon dioxide byproduct, including in cement,lime, iron, and steel manufacturing. The United States EnvironmentalProtection Agency (EPA) and the United Nations Intergovernmental Panelon Climate Change (IPCC) classify emissions based on fuel combustion(which predominantly includes motor vehicle and power plants) and otherindustrial sources. 97% of anthropogenic CO₂ emissions in the UnitedStates are attributed to fossil-fuel combustion sources, such as powerplants, incinerators, and motor vehicles. Other significant pointsources of carbon dioxide include cement, lime, and iron/steelmanufacturers, all of which generate copious CO₂ during processing, bothas a reaction byproduct and through burning of hydrocarbon fuels.

In addition to being an undesirable greenhouse gas, CO₂ has thepotential to create operational and economic issues, as it is a diluentwithout any fuel value. It is an acid gas and can cause corrosionproblems in the presence of water, creating carbonic acid that can bequite corrosive to some alloys.

Through international treaties, such as the Kyoto Protocol, numerousnations have committed to reducing emissions of various greenhousegases, including CO₂. In the United States, there has traditionally beena great focus on developing equipment to effectively reduce emissions ofregulated air pollutants, such as particulate matter, sulfur oxides, andnitrogen oxides. However, development of abatement technology forunregulated CO₂ emissions has lagged behind other control technology.However, as various nations implement regulations and trading programsthat restrict the generation of various greenhouse gases, in particularCO₂, there is an emerging need for more effective and inexpensive CO₂abatement technologies.

Existing methods for the removal of CO₂ from gas streams includechemical absorption/adsorption with particular solvent systems (aminescrubbing), membrane separation, cryogenic fractionation, and/oradsorption using molecular sieves. In disposable systems, the activematerial(s) will make a single pass through the reactor/scrubber and isthen discarded. One-time use systems are less desirable due to the addedexpense and maintenance associated with the disposal of larger amountsof spent active material. Regenerative systems are designed toregenerate the active material, making it suitable for subsequentproductive passes through the reactor. Molecular sieves, such aszeolites and activated carbon, are used in regenerative pressure swingadsorption (PSA) or temperature swing adsorption systems which separategas mixtures by selective adsorption of one or more of the gases at highpressure and/or low temperature, to remove the undesirable componentsfrom a gas stream. The captured impurities are then desorbed by loweringthe pressure, or increasing the temperature, of the adsorbent system(thus the system “swings” from a high to low pressure or a low to hightemperature). The desorption step regenerates the adsorbent material forreuse during the subsequent adsorption step. PSA systems typicallycomprise several adsorption beds, through which the gas stream ispassed, allowing for separation of the selected gas species. Each of theabove processes has drawbacks, including high capital investment andoperating costs, as well as relatively small throughput capacity and lowremoval efficiency in some cases. Such systems are potentiallycost-prohibitive for various applications, in particular for highthroughput manufacturing facilities that generate high quantities ofcarbon dioxide and other emissions.

Thus, there is a need for processes that reduce CO₂ emissions fromexhaust gases of stationary sources in an efficient manner and further,are cost-effective. Additionally, CO₂ emission abatement equipment canpreferably handle high flow rates associated with industrialapplications while achieving desirable removal efficiencies. Preferably,such abatement processes are regenerative and employ recycling to embodysustainable development initiatives.

SUMMARY

In various aspects, the present disclosure provides methods forsequestering carbon dioxide as a pollutant present in an industrialeffluent fluid stream containing carbon dioxide. In one aspect, a methodcomprises reducing an amount of carbon dioxide in the fluid stream bycontacting the stream with a scrubbing material. The scrubbing materialcomprises a first component and a second component. In certain aspects,the reaction is conducted in the presence of water (for example, inslurry or semi-dry forms). The first component is distinct from thesecond component. Further, the first component comprises a source ofcalcium oxide and a source of alkali metal ions and the second componentcomprises a slag having one or more reactive silicate compounds.

In certain embodiments, the first component comprises a materialselected from the group consisting of: cement kiln dust (CKD), lime kilndust (LKD), sugar beet lime, clinker dust, slaked lime, quick lime, andmixtures thereof. In some embodiments, the second component comprises amaterial selected from the group consisting of blast furnace slag, steelslag, and mixtures thereof. Examples of suitable slag material include:air cooled blast furnace slag, granulated blast furnace slag, groundgranulated blast furnace slag, expanded and/or pelletized blast furnaceslag, basic oxygen furnace steel slag, open hearth furnace steel slag,electric arc furnace steel slag, and any mixtures thereof. The secondcomponent may optionally comprise a stainless steel slag derived from afurnace manufacturing and/or processing stainless steel. In certainembodiments, the first component comprises cement kiln dust (CKD) andthe second component comprises a stainless steel slag. In variousaspects, the methods produce a product comprising calcium carbonate andspent scrubbing material. In certain embodiments, the calcium carbonateproduct is recycled as a raw material in an industrial process. Oneexample of such recycling is using the calcium carbonate product as araw material for cement manufacturing or lime manufacturing. The calciumcarbonate product may optionally be used as a flux material in ironand/or steel processing.

In various aspects, a carbon dioxide sequestration material slurry isprovided for scrubbing carbon dioxide from a carbon dioxide containingfluid stream. The slurry comprises a first component, a secondcomponent, and water. The first component comprises one or morematerials selected from the group consisting of: cement kiln dust, limekiln dust, sugar beet lime, clinker dust, quick lime, slaked lime, andmixtures thereof. The second component comprises a slag having a sourceof reactive silicates. The slurry comprises particles having an averagemaximum particle size of less than or equal to about 500 μm and anaverage surface area of greater than or equal to about 1000 cm²/g.

In yet other embodiments, a carbon dioxide sequestration material isprovided in the form of a slurry for scrubbing carbon dioxide from acarbon dioxide containing fluid stream. The slurry comprises a firstcomponent comprising cement kiln dust (CKD) and a second componentcomprising a slag having a source of reactive silicates. The slurry alsocomprises water. The slurry comprises particles having an averagemaximum particle size of less than or equal to about 500 μm and anaverage surface area of greater than or equal to about 1000 cm²/g.

In another aspect, the disclosure provides a carbon dioxide emissionabatement system. The system comprises a reaction chamber. The reactionchamber has a fluid inlet, a slurry inlet, a mixing zone, a fluidoutlet, and a slurry outlet. A carbon dioxide containing effluent streamis in fluid communication with the reaction chamber and is introduced tothe reaction chamber via the fluid inlet. Further, a source of slurry isin fluid communication with the reaction chamber. A slurry from thesource of slurry is introduced to the reaction chamber via the slurryinlet. Moreover, the mixing zone provides turbulent mixing of the slurryand the effluent stream. The reaction chamber has a volume such that itprovides a sufficient residence time to treat the effluent stream toreduce an amount of carbon dioxide by at least about 30%. The slurrycomprises a first component comprising a source of calcium oxide and asource of alkali metal ions, a second component comprising a slag havinga source of reactive silicates, and water. A spent slurry and/or acalcium carbonate product is removed from the reaction chamber via theslurry outlet.

In other embodiments, a method of recycling industrial byproducts isprovided. A carbon dioxide scrubbing material is formed by admixing afirst manufactured component with a second manufactured component. Thefirst component comprises a source of calcium oxide and a source ofalkali metal ions. The second component comprises a slag having one ormore reactive silicate compounds. An effluent stream generated in anindustrial process comprising carbon dioxide is then contacted with thescrubbing material. A product comprising calcium carbonate is generatedthat is capable of beneficial reuse such as in an industrial process. Incertain embodiments, after the contacting and after the generating, thescrubbing material is spent and at least a portion of the spentscrubbing material is admixed with fresh first manufactured componentand fresh second manufactured component.

In various other aspects, the disclosure provides methods of reducingcarbon dioxide emissions from effluent streams generated by stationarycombustion sources (e.g., boilers, incinerators), cement kilns, limekilns, iron furnaces and steel furnaces. In this manner, various aspectsof the disclosure provide an effective means for removing carbon dioxideemissions, thus controlling greenhouse gas emissions, while furtherrecycling at least one industrial byproduct, and preferably multiplebyproduct materials, to form a useful product.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is an exemplary process flow diagram for a carbon dioxidesequestration system according to certain embodiments of the disclosure;

FIG. 2 is a schematic illustration of one embodiment of the presentdisclosure showing a carbon dioxide emission abatement system with ascrubber tower reactor;

FIG. 3 is a process flow diagram for certain embodiments of thedisclosure showing a carbon dioxide removal system, where a treatedeffluent stream exiting a carbon dioxide removal device is furthertreated with an air pollution control device to remove one or moreadditional pollutants other than carbon dioxide; and

FIG. 4 is a process flow diagram for certain other embodiments of thedisclosure showing a carbon dioxide removal system, where an effluentstream is pre-treated by an air pollution control device to remove oneor more pollutants prior to entering a carbon dioxide removal device.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Itshould be understood that throughout the drawings, correspondingreference numerals indicate like or corresponding parts and features.

In various aspects, the teachings of the disclosure provide a processfor reducing an amount of gaseous carbon dioxide present in a fluidstream by sequestering or scrubbing carbon dioxide from the gas phase ofthe fluid stream. In certain embodiments, the fluid stream comprises agas and/or vapor, but may also have entrained solids and/or liquids,such as entrained particulates, liquid droplets and/or aerosols. Invarious embodiments, the fluid stream is an effluent stream or anexhaust stream generated in an industrial process. The fluid stream iscontacted with a carbon dioxide scrubbing or sequestration material toremove carbon dioxide. After contact with the scrubbing material, theamount of carbon dioxide present in the fluid stream is reduced. Incertain embodiments, the carbon dioxide reacts with the scrubbingmaterial to form a useful product that will be described in more detailbelow.

In various aspects, the scrubbing material comprises a first component,a second component and water. The first component is distinct from thesecond component. In various embodiments, the first component comprisesa source of calcium oxide and a source of alkali metal ions. The secondcomponent comprises a slag having one or more reactive silicatecompounds. The scrubbing material reacts with carbon dioxide to form aproduct comprising calcium carbonate and spent scrubbing material.

In various embodiments, the first component of the scrubbing materialcomprises calcium oxide (CaO). Further, it is preferred that the firstcomponent also comprises a source of alkali metal ions, such as sodiumand/or potassium ions, for example. In certain embodiments, the firstcomponent comprises a material that is generated or manufactured in anindustrial process. As will be described in more detail below, someembodiments employ a beneficial reuse for waste materials that wouldotherwise be discarded, stockpiled, or land-filled. However, varioussuitable sources of calcium oxide and alkali metal ions may be naturallyoccurring materials, such as minerals, or may be manufactured commercialproducts. In various aspects, the first component comprises a materialselected from the group consisting of cement kiln dust, lime kiln dust,sugar beet lime, clinker dust, slaked lime, quick lime, and any mixturesthereof. Such mixtures encompass any combination of two or morecomponents. In certain embodiments, the first component comprises amaterial selected from the group consisting of cement kiln dust, limekiln dust, sugar beet lime, and mixtures thereof. In other embodiments,the first component comprises lime kiln dust. In certain embodiments,the first component comprises cement kiln dust. Such non-limitingmaterials are suitable sources of calcium oxide and alkali metal ionsfor use in the scrubbing materials. The first component can compriseother sources of calcium oxide and alkali metal ions, including by wayof example, waste water treatment plant sludge, pulp and paper sludge,calcium carbide manufacturing byproducts, and other materials providingcalcium oxide and alkali metal ions, as are well known to the skilledartisan.

As appreciated by one of skill in the art, many of the sources ofcalcium oxide and alkali metal ions can have varied compositions,depending on the particular process in which they are made; the specificcompositions of raw materials and fuels that are employed to manufacturethe source; the conditions and duration that the material is stored orstockpiled; as well as a variety of other factors.

In this regard, in some embodiments, the first component preferablycomprises one or more active ingredients selected from the groupconsisting of: CaO, K₂O, Na₂O, and mixtures thereof. In certainembodiments, the first component comprises one or more activeingredients selected from the group consisting of: CaO, Na₂O, K₂O, andmixtures thereof, where a total amount of the active ingredients presentin the scrubbing material is at about 30% to about 60% by weight. Thefirst component optionally comprises additional active compounds inaddition to the calcium oxide and alkali oxides and such activeingredients are not restricted to those recited above.

In certain aspects, the first component comprises calcium oxide (CaO) atgreater than or equal to about 30% by weight. As used herein, allpercentages are on a weight basis, unless indicated as otherwise. Itshould be noted that the chemical compositions of various materialsdescribed herein are expressed in terms of simple oxides calculated fromelemental analysis, typically determined by x-ray fluorescencetechniques. While the various simple oxides may be, and often are,present in more complex compounds in the material, the oxide analysis isa useful method for expressing the concentration of compounds ofinterest in the respective compositions.

In some embodiments, the first component comprises free lime (free CaO)at greater than or equal to about 3% by weight. “Free lime” refers tothe free calcium oxide (free CaO) readily available in a material for ahydration reaction with water. Unslaked lime, also referred to as quicklime, contains a high concentration of dehydrated (free) lime or calciumoxide (CaO) that can undergo reaction with water, i.e., slaking. Incontrast, a slaked or hydrated lime has already been reacted with waterto form Ca(OH)₂. Free lime content is often used as an indicator of thereactivity of the calcium oxide containing materials. In certainembodiments of the disclosure, the free lime may be about 5% or evengreater.

In some embodiments, the first component preferably comprises an amountof alkali ion source in the form of sodium oxide (Na₂O) and/or potassiumoxide (K₂O) at greater than or equal to about 1% by weight. It should benoted that some alkali metal ions complex with various complex anions,such as sulfates, however, a typical analysis of alkali contentexpresses the alkali metal oxides and sulfates individually. In certainembodiments, the amount of alkali ion source in the form of sodium oxide(Na₂O) and/or potassium oxide (K₂O) is greater than or equal to about 3%by weight; optionally greater than or equal to about 4% by weight. Thealkali content of various pozzolanic and/or cementitious materials canalso be expressed as a sodium equivalent (Na₂O_(e)) which accounts forthe presence of both Na₂O and K₂O calculated by the equationz=x+(0.658·y)  (EQN. 1)where z is the sodium equivalent Na₂O_(e), x is the weight percent ofNa₂O present in the composition, and y is the weight percent of K₂Opresent in the composition. Such sodium equivalents Na₂O_(e) may rangefrom greater than 0.01%, to greater than or equal to about 1% by weight,optionally greater than or equal to about 2% by weight, optionallygreater than or equal to about 3% by weight, and in some embodiments,greater than or equal to about 5% by weight.

As will be discussed in greater detail below, the alkali metal ionspromote desirable reaction conditions for the scrubbing material, suchas providing a high pH that is believed to provide a faster rate ofreaction and to favor formation of preferred products in the scrubbingmaterial reaction with carbon dioxide.

In certain embodiments, the first component has a composition as setforth in Table I, exclusive of impurities and diluents.

TABLE I Oxide Approximate Weight % Calcium Oxide (CaO) 30-45 Silica(SiO₂) 10-20 Aluminum Oxide (Al₂O₃) 2-7 Iron Oxide (Fe₂O₃) 1-3 MagnesiumOxide (MgO) 0.5-3  Sulfate (SO₃)  1-15 Sodium Oxide (Na₂O) 0.1-1 Potassium Oxide (K₂O) 0.1-15 

In some embodiments, the first component preferably comprises cementkiln dust (CKD), which generally refers to a byproduct generated withina cement kiln or related processing equipment during Portland cementmanufacturing. Portland cement can be manufactured in a wet or a dryprocess kiln. While the wet and dry processes differ, both processesheat the raw material in stages. Cement manufacturing raw materialscomprise sources of calcium, silica, iron, and alumina, and usuallyinclude limestone, as well as a variety of other materials, such asclay, sand and/or shale, for example.

The first stage of cement manufacturing is a pre-heating stage thatdrives off any moisture from the raw materials, removes water ofhydration, and raises the material temperature up to approximately 1500°F. (approximately 800° C.). The second stage is the calcination stagewhich generally occurs between about 1500° F. and 2000° F.(approximately 1100° C.), where the limestone (CaCO₃) is converted tolime (CaO) by driving off carbon dioxide (CO₂) in a calcinationreaction. The raw materials are then heated to a maximum temperature ofbetween about 2500° F. to 3000° F. (approximately 1400° C. to 1650° C.)in the burning zone, where they substantially melt and flux, thusforming inorganic compounds, such as tricalcium silicate, dicalciumsilicate, tricalcium aluminate, and tetracalcium aluminoferrite. Atypical analysis of portland cement products shows that they containapproximately 65-70% CaO, 20% SiO₂, 5% Al₂O₃, 4% Fe₂O₃, with lesseramounts of other compounds, such as oxides of magnesium, sulfur,potassium, sodium, and the like. The molten raw material is cooled tosolidify into an intermediate product in small lumps, known as “clinker”that is subsequently removed from the kiln. Clinker is then finelyground and mixed with other additives (such as a set-retardant, gypsum)to form Portland cement, which can then be mixed with aggregates andwater to form concrete.

Generally, CKD comprises a combination of different particles generatedin different areas of the kiln, pre-treatment equipment, and/or materialhandling systems, including for example, clinker dust, partially tofully calcined material dust, and raw material (hydrated and dehydrated)dust. As appreciated by those of skill in the art, the composition ofthe CKD varies based upon the raw materials and fuels used, themanufacturing and processing conditions, and the location of collectionpoints for CKD within the cement manufacturing process. CKD can includedust or particulate matter collected from kiln effluent (i.e., exhaust)streams, clinker cooler effluent, pre-calciner effluent, air pollutioncontrol devices, and the like. Clinker cooler dust refers to dustcollected in the clinker cooler areas of the kiln and typically has achemical composition that is very similar to Portland cement.

While CKD compositions will vary for different kilns, CKD usually has atleast some cementitious and/or pozzolanic properties, due to thepresence of the dust of clinker and calcined materials. Typical CKDcompositions comprise silicon-containing compounds, such as silicatesincluding tricalcium silicate, dicalcium silicate; aluminum-containingcompounds, such as aluminates including tricalcium aluminate; andiron-containing compounds, such as ferrites including tetracalciumaluminoferrite. CKD generally comprises relatively high amounts ofcalcium oxide (CaO). Exemplary CKD compositions comprise calcium oxideat about 10 to about 60% by weight, optionally about 25 to about 50% byweight, and optionally about 30 to about 55% by weight. In someembodiments, CKD comprises a concentration of free lime of about 1 toabout 10%, optionally of about 1 to about 5%, and in some embodimentsabout 3 to about 5%. Further, CKD typically comprises sodium andpotassium alkali metal ions respectively at about 0.1 to about 10% byweight, and optionally about 0.2 to about 5% by weight. CKD may compriseadditional alkali metal ions, alkaline earth metal ions, and sulfur,inter alia. CKD also typically comprises silica (SiO₂) at about 10 toabout 20% by weight, alumina (Al₂O₃) at about 2 to about 7% by weight,and iron oxide (Fe₂O₃) at about 1 to about 3% by weight.

Exemplary CKD dusts have specific gravity ranges from about 2.6 to 2.8,a maximum particle size of about 0.30 mm (300 μm) and Blaine fineness(specific surface area) ranging from about 4,600 to about 14,000 cm²/g.

In certain embodiments, the first component of the scrubbing material ofthe disclosure comprises lime (i.e., quick lime) or lime kiln dust(LKD). LKD is a byproduct from the manufacturing of lime. LKD is dust orparticulate matter collected from a lime kiln or associated processingequipment. Manufactured lime can be categorized as high-calcium lime ordolomitic lime, and LKD varies based upon the processes that form it.Lime is often produced by a calcination reaction conducted by heatingcalcitic raw material, such as calcium carbonate (CaCO₃), to form freelime CaO and carbon dioxide (CO₂). High-calcium lime has a highconcentration of calcium oxide and typically some impurities, includingaluminum-containing and iron-containing compounds. High-calcium lime istypically formed from high purity calcium carbonate (about 95% purity orgreater). Typical calcium oxide content in an LKD product derived fromhigh-calcium lime processing is similar to the concentration of calciumoxide in the lime product itself, and can be greater than or equal toabout 75% by weight, optionally greater than or equal to about 85% byweight, and in some cases greater than or equal to about 90% by weight.In some lime manufacturing, dolomite (CaCO₃.MgCO₃) is decomposed byheating to primarily generate calcium oxide (CaO) and magnesium oxide(MgO), thus forming what is known as dolomitic lime. In lime or LKDgenerated by dolomitic lime processing, calcium oxide can be present atgreater than or equal to about 45% by weight, optionally greater than orequal to about 50% by weight, and in certain embodiments, greater thanor equal to about 55% by weight. While both lime and LKD vary based uponthe type of lime processing employed, they generally have relativelyhigh concentrations of free lime. Typical amounts of free lime in suchlime or LKD products are about 10 to about 50%, optionally about 20 toabout 40%.

Further, LKD and lime products typically comprise sodium and potassiumalkali metal ions at respective amounts of about 0.01 to about 1% byweight, and optionally about 0.03 to about 0.25% by weight. Lime and/orLKD may comprise additional alkali metal ions, alkaline earth metal ions(such as the MgO described above), and sulfur, inter alia. LKD alsocomprises silica (SiO₂) at about 1 to about 10% by weight, alumina(Al₂O₃) at about 0.1 to about 5% by weight, and iron oxide (Fe₂O₃) atabout 0.5 to about 2% by weight. Exemplary LKDs have specific gravityranging from about 2.6 to 3.0, a maximum particle size of about 2 mm(2,000 μm) and Blaine fineness (specific surface area) ranging fromabout 1,300 to about 10,000 cm²/g.

Another exemplary material for use as a first component of the scrubbingmaterial of the present disclosure is a sugar refining lime byproduct.Lime is used in the production of sugar derived from sugar cane, sugarbeets, maple sap and sorghum. For example, sugar cane and sugar beetsare harvested and processed with water to form raw juice, which has lowpH and contains dissolved impurities. The sugar juice thus containssucrose, pulp, various non-sugars, e.g., organic and inorganic salts,amino acids, dyes and high molecular substances, such as protein andpectin. Hydrated lime is added to the juice to raise the pH and to reactwith the impurities to form insoluble calcium organic compounds that canbe removed. In a conventional sugar purification method, lime (CaO) andcarbon dioxide (CO₂) are added, which results in the formation of aprecipitate (sludge) consisting of calcium carbonate and part of theabove-mentioned non-sugar components. The dewatered sludge comprisescalcium oxide (CaO), usually in hydrated form (Ca(OH)₂). The sugar juicemay be further successively refined in this manner. Sugar beets tend torequire the greatest amount of refinement with lime, and the sludgebyproduct is generally referred to as “sugar beet lime.” However, theuse of the term “sugar beet lime” is merely representative of the classof the sugar processing lime byproducts that are suitable for use in thescrubbing materials of the disclosure.

In sugar beet lime, calcium oxide can be present at greater than orequal to about 25% by weight, optionally greater than or equal to about30% by weight, and in certain embodiments, greater than or equal toabout 40% by weight. Sugar beet lime also typically comprises alkalimetal ions, such as sodium and potassium, respectively present at about0.01% by weight or greater; optionally greater than or equal to about0.05% by weight, optionally greater than or equal to about 0.1% byweight, and in some embodiments greater than or equal to about 1% byweight of the composition.

Thus, the first component of the scrubbing material may comprise anysuitable source of calcium oxide and alkali metal ions. The firstcomponent can optionally comprise a single suitable material or mixturesof suitable materials that provide calcium oxide and alkali metal ionsat the desired concentrations.

Slag materials are industrial byproducts of metal manufacturing. Invarious embodiments, the second component of the scrubbing materialcomprises such a slag material that provides a reactive silicate.Silicates are typically in a tetrahedral form that can be joined inchains, double chains, sheets, three-dimensional networks, and otherpolymerization (“geo-polymer”) forms. A silicate comprises silicon andoxygen atoms with one or more metals and/or hydrogen. Generally, thesilicon and oxygen are in the form of Si_(x)O_(y), where x is generally1 or 2 and y can range from 2 to 7 (i.e., SiO₂, SiO₃, SiO₄, and Si₂O₇).While many silicates are insoluble or stable in water, it is believedthat basic conditions and increased temperatures facilitate greatersolubility and/or reactivity of certain silicate compounds in thepresence of water. The water solubility and/or reactivity of thesilicate compound in the presence of water depends upon numerousfactors, including the cations with which the silicate anion iscomplexed (for example, Group IA alkali metal ion elements and NH₄ ⁺tend to form water soluble silicates).

Certain silicate species are more reactive with ionic species and mayexhibit higher solubility in water, where such silicates are believed toionize to form SiO⁻ ions. For example, silicates can form variouscrystal structures, ranging from crystalline and highly-ordered phases(for example quartz) to crypto-crystalline phases (for example,extremely fine crystalline structures like chalcedony) to amorphousphases or glassy non-crystalline structures (for example, opal). It isbelieved that amorphous lattice structures permit higher ionic attackand breakdown of the silicate network. Thus, highly ordered andwell-crystallized phases are stable and non-reactive, as wherecrypto-crystalline and amorphous silicate lattices are susceptible toattack due to disordered and open lattice structures, hence suchsilicates are reactive.

In accordance with various embodiments of the disclosure, the secondcomponent of the scrubbing material comprises reactive silicates. Whilenot limiting as to any theory by which the present teachings operate, itis believed that certain crystalline phases of dicalcium silicate (2CaO.SiO₂ typically expressed in shorthand as C₂S) and tricalciumsilicate (3CaO.SiO₂ typically expressed in shorthand as C₃S), inparticular the γ-C₂S, β-C₂S, and C₃S crystalline phases, are reactivesilicates that can be formed in slag materials, and thus suitably reactwith carbon dioxide in the presence of water. By reactive silicatecompound, it is meant that more than 10% of the total silicate compoundspresent in a material will react with carbon dioxide in the presence ofwater at 25° C. (77° F.) and ambient pressure at pH of greater than orequal to about 9.

Further, in accordance with various embodiments of the disclosure, suchsilicate compounds have higher reactivity in water when pH is basic.Preferably, the pH of the scrubbing material is greater than or equal toabout 7, more preferably greater than or equal to about 9, and in someembodiments about 11 up to about 14 to enhance the solubility ofsilicate compound. Practically, the pH in such systems does not usuallyexceed about 13. Increased temperatures also increase solubility ofsilicate compounds in water. In accordance with various embodiments ofthe disclosure, it is preferred that the slag of the second compositioncomprises greater than or equal to about 5% reactive silicates,optionally greater than or equal to about 10%; optionally greater thanor equal to about 15% of reactive silicates by weight.

Various slag materials comprise calcium silicates. Preferably, at leasta portion of these calcium silicates are reactive with carbon dioxideand/or calcium oxide in the presence of water in the scrubbing materialsof the various embodiments of the disclosure. As described above, thefirst component of the scrubbing material preferably comprises both asource of calcium oxide and alkali metal ions, which provide an alkalineor basic pH in the scrubbing material to enhance the solubility of thereactive silicate compounds.

By way of background, slags are generally byproduct compounds generatedby metal manufacturing and processing. The term “slag” encompasses awide variety of byproduct materials, typically comprising a largeportion of the non-metallic byproducts of ferrous metal and/or steelmanufacturing and processing. Generally, slagging agents, or fluxmaterials, are added to furnaces to strip impurities from the molteniron ore, steel scrap, iron and/or steel feed stock during processing.Typical flux materials are limestone (CaCO₃) and/or dolomite(CaCO₃.MgCO₃). Molten slag forms as a silicate melt floating to the topof the furnace that cools to form complex silicates and oxides. Thecomposition of slag is dependent upon the metal being processed in thefurnace and often contains metal sulfides and metal atoms in anelemental form. The composition and properties of the slag also varybased on the type of furnace and the post-processing treatment, whichcan affect not only the chemical composition, but the crystallinity,phase development, and surface morphology that can impact reactivity.For example, as discussed above, it is preferred that one or morereactive silicate phases are formed in the slag, such as γ-C₂S, β-C₂S,and C₃S. Further, the particle size, porosity, and surface area of theslag impacts the reactivity, as lower particle size, higher porosity andhence higher surface area materials enable greater exposure to CO₂ andwater to facilitate greater reaction.

Blast furnaces process iron ore to form refined pig iron. Blast furnaceslags are generally formed into three main types: air-cooled,granulated, and pelletized (or expanded). Air-cooled blast furnace slagis formed by allowing the molten slag to cool relatively slowly underambient conditions, while the final cooling can be accelerated with acooling process, such as water spray. Granulated slag is formed byquenching molten slag in water, thus forming small disordered-structureglass particles. Such granulated slag is often further ground, therebyenhancing the cementitious properties of the material. Pelletized orexpanded slag is cooled through a water jet, which leads to rapid steamgeneration that develops extensive vesicle structures in the material.

Steel slags are formed during the further processing of pig iron andother steel materials in steel-making furnaces. Typical steel furnacesinclude basic oxygen process furnaces (BOF), open hearth furnaces (OHF),and electric arc furnaces (EAF). Most steel is now made in integratedsteel plants using a version of the basic oxygen process or in specialtysteel plants that use an electric arc furnace process. Open hearthfurnace processes are less prevalent. In an exemplary basic oxygenprocess, hot liquid blast furnace metal, scrap, and fluxes are chargedto a converter (furnace). A lance is lowered into the converter andhigh-pressure oxygen is injected. The oxygen combines with and removesthe impurities in the charge. These impurities consist of carbon asgaseous carbon monoxide, and silicon, manganese, phosphorus and someiron as liquid oxides, which combine with lime and/or dolomite to formthe steel slag. At the end of the refining operation, the liquid steelis poured into a ladle while the steel slag is retained in the vesseland subsequently tapped into a separate slag pot.

Many different grades of steel can be produced and the properties of thesteel slag can change significantly with each grade. Grades of steel canbe classified as high, medium, and low, depending on the carbon contentof the steel. High-grade steels have high carbon content. To reduce theamount of carbon in the steel, greater oxygen levels are required in thesteel-making process. This also requires the addition of increasedlevels of flux material for the removal of impurities from the steel andincreased slag formation.

Steel furnace slag typically contains much higher amounts of dicalciumsilicate and calcium oxide. There are several different types of steelslag produced during the steel-making process, including furnace (ortap) slag, raker slag, synthetic (or ladle) slags, and pit (or cleanout)slag. The steel slag produced during the primary stage of steelproduction is referred to as furnace slag or tap slag. After beingtapped from the furnace, the molten steel is transferred in a ladle forfurther refining to remove additional impurities still contained withinthe steel, which generates additional steel slags by again adding fluxesto the ladle to melt. These slags are combined with any carryover offurnace slag and assist in absorbing deoxidation products (inclusions),heat insulation, and protection of ladle refractory. The steel slagsproduced at this stage of steel making are generally referred to asraker and ladle slags. Pit slag and clean out slag are other types ofslag commonly found in steel-making operations. They usually consist ofthe steel slag that falls on the floor of the plant at various stages ofoperation, or slag that is removed from the ladle after tapping. Theladle refining stage usually involves comparatively high flux materialaddition and the properties of these synthetic slags are oftensignificantly different from those of the furnace slag. Such slags areoften rich in calcium oxide and silicates and are well suited as amaterial for the second component of the scrubbing material,particularly as these synthetic slags cannot generally be recycled asaggregates due to expansion in situ.

It should be noted that the second component may comprise a combinationof slags originating from different locations of the furnace and/orprocessing or may include combinations of slags from different furnacesor processes. The term furnace encompasses both iron ore and steelconverters. Generally, blast furnace slags refer to those generated iniron ore furnaces and steel slags are those generated by any steelforming or refining process, including stainless steel slags, as will bedescribed in more detail below. Depending on the location from whichthey originate in the process and subsequent processing, many of theslags have different particle size distributions, different mineralogyand crystal formation. These slags may be further ground to achievedesirable particle size distributions and/or fineness (surface area).

Exemplary slags comprise calcium-containing compounds,silicon-containing compounds, aluminum-containing compounds,magnesium-containing compounds, iron-containing compounds,manganese-containing compounds and/or sulfur-containing compounds. Incertain embodiments of the disclosure, the slag material(s) of thesecond component are selected to comprise calcium oxide at about 25 toabout 60%, optionally about 30 to about 50%, and optionally about 30 toabout 45% by weight. In various embodiments, the second componentcomprises silicon dioxide (SiO₂) at greater than or equal to about 25%by weight; optionally greater than or equal to about 30% by weight;optionally greater than or equal to about 35% by weight. It should benoted that the amount of SiO₂ present in the composition is reflectiveof the simple oxide analysis (as discussed above in the context of thefirst component) and does not necessarily reflect the concentration ofreactive silicates, which may only form a portion of the total amount ofSiO₂ present in the material. In certain embodiments, the secondcomponent further comprises calcium oxide (CaO) at greater than or equalto about 25%; optionally greater than or equal to about 30% by weight;optionally greater than or equal to about 35% by weight. As discussedabove, the calcium oxide and silicon oxide are typically present in theform of calcium silicates, however, based on the overall simple oxideanalysis, are present at respective amounts of greater than or equal toabout 25% by weight. In certain embodiments, the second componentcomprises one or more active ingredients selected from CaSiO₃, CaO, andmixtures thereof, where a total amount of the active ingredient presentin the second component is about 35 to about 90% by weight.

In certain embodiments, the second component comprising a slag has acomposition as set forth in Table II, exclusive of impurities anddiluents.

TABLE II Oxide/Metal Approximate Weight % Calcium Oxide (CaO)  35-55Silica (SiO₂)  10-35 Aluminum Oxide (Al₂O₃) 0.1-10 Iron Oxide (FeO)0.1-40 (70-80% FeO & 20-30 Fe₂O₃) Magnesium Oxide (MgO)  3-10 ManganeseOxide (MnO)  3-10 Sulfate (SO₃) 0.01-15  Phosphate (P₂O₅) 0.01-1 Metallic Iron 0.5-10

One example of a suitable slag generally having cementitious propertiesand reactive silica is ground granulated blast furnace slag (GGBFS). Thecooling rate of slag is typically sufficiently low so that variouscrystalline compounds are generally formed, including predominantcompounds such as dicalcium silicate, tricalcium silicate, dicalciumferrite, meriwinite, calcium aluminate, calcium-magnesium iron oxide,free lime, and free magnesia. The free lime and magnesia are believed tobe responsible for expansion of most steel slags when they exposed tomoisture, typically making them unsuitable for many applications, suchas aggregates. However, in the context of the present disclosure, theseotherwise undesirable materials can be recycled and employed for abeneficial use.

Stainless steel slags are particularly preferred materials for thesecond component of certain embodiments of the disclosure, as theytypically comprise higher concentrations of free lime and/or freemagnesia, and relatively high concentrations of silicates, particularlyin the reactive silicate crystalline form of γ-C₂S. During crystaldevelopment and phase transition, this γ-C₂S phase is believed to causeinstability in the C₂S crystal lattice that causes fragmentation to finepowder form due to self-pulverization.

As appreciated by those of skill in the art, varying amounts ofelements, such as nickel, chromium, molybdenum, and manganese, can beadded to refined iron to form steel: the greater the amounts of theseelements that are included, the higher the grade of steel. Theseelements tend to be incorporated into the compounds present in the slagthat is used to refine the metals. In general, stainless steel containsat least about 10.5% chromium. A typical austenitic steel has chromiumat greater than or equal to about 16% and nickel at greater than orequal to about 8%. Stainless steel comprises carbon up to about 1.7% byweight. Higher grades of stainless steel usually have lower carboncontents and may contain molybdenum and manganese, inter alia. By way ofexample, a low Grade 304 austenitic stainless steel has carbon (C) atless than or equal to 0.08%, chromium (Cr) from between about 17 to19.5%, nickel (Ni) from about 8 to 10.5%, manganese (Mn) at less than orequal to about 2%, with no molybdenum (Mo). Another exemplary highergrade steel is 316L where carbon (C) is present at less than or equal to0.03%, chromium (Cr) at about 17%, nickel (Ni) at about 9%, manganese(Mn) at about 2%, and molybdenum (Mo) at about 2.5%. “L” designates lowcarbon content. A higher grade austenitic stainless steel is Grade317LMN that has carbon (C) at less than or equal to 0.03%, chromium (Cr)from between about 16.5 to 18.5%, nickel (Ni) from about 13.5 to 17.5%,manganese (Mn) from about 1 to 2%, and molybdenum (Mo) from about 4 to5%. In the 317LMN grade, the “M” and “N” designations indicate that thecomposition contains increased levels of molybdenum and nickelrespectively. Stainless steel slags tend to incorporate these variouselements and further comprise a high amount of reactive and/or watersoluble silicates, which are highly desirable for scrubbing materials invarious embodiments of the disclosure.

The second component can further comprise other sources of reactivesilicates, in addition to the slag described above, so long as theycontribute desirable and/or necessary active ingredients discussedabove. For example, other suitable examples include blast (cupola)furnace dust collected from air pollution control devices attached toblast furnaces, such as cupola arrester filter cake. Another suitableindustrial byproduct source is paper de-inking sludge ash. As recognizedby those of skill in the art, there are many differentmanufactured/industrial process byproducts that are feasible as a sourceof reactive silicates of the scrubbing material of the disclosure. Manyof these well known byproducts comprise alumina and/or silica, as well.Combinations of any of the exemplary manufactured products and/orindustrial byproducts are contemplated for use in certain embodiments ofthe disclosure.

Thus, the scrubbing materials of the disclosure comprise the firstcomponent comprising a source of calcium oxide and a source of alkalimetal ions and the second component comprises a slag comprising reactivesilicates. In certain embodiments, a ratio of the first component to thesecond component in the scrubbing material is about 10:1 to about 1:10.In certain embodiments, a ratio of the first component to the secondcomponent in the slurry is about 3:4 to about 4:3. While not limiting toany particular theory, it is believed that an increased rate of reactionand a higher reaction conversion of carbon dioxide with calcium oxideand silicates occurs in a scrubbing material when the molar amount ofavailable calcium is higher that available silicon. Thus, where activeingredients in the scrubbing material are calcium oxide and silicondioxide, a molar ratio of calcium (Ca) to silicon (Si) in the scrubbingmaterial is preferably about 1:1 to about 10:1 in certain embodiments tofacilitate reaction with carbon dioxide.

The scrubbing materials of various embodiments preferably comprisewater. The water facilitates transport, solubilization, and ionizationof the various active compounds of the present disclosure. In variousembodiments, the scrubbing material is provided in the form of a slurry.Slurry is formed by combining water with the first and second componentsdescribed herein. A slurry is a mixture of soluble compounds andsuspended insoluble particles. The amount of water in the slurry rangesfrom 5% or 10% on the low side up to 90% or 95% by weight on the highside. In various embodiments, the slurry has a water content of greaterthan or equal to about 15% by weight or greater than or equal to about20% by weight; in certain embodiments greater than or equal to about 30%by weight; and in some embodiments greater than or equal to about 40% byweight. In certain embodiments, the water content of the scrubbingmaterial is about 15% to about 85% by weight, and in exemplaryembodiments the slurry contains from 20% to 85%, from 30% to 85%, from40% to 85%, or from 50% to 85% by water. In various embodiments, theslurry contains 80% or less by weight water or 70% or less by weightwater. As the water content increases, the viscosity of the slurrydecreases, thus pumping and handling become easier. In certain aspects,the slurry has a viscosity that permits pumping and mass transport as aliquid through various parts of the system.

Where the scrubbing material is in a slurry form and has a relativelyhigh water content, the mass transport of carbon dioxide from the gasstream to the liquid/solid phase of the slurry is enhanced, which isdesirable, particularly in applications where the fluid stream has ahigh velocity. Further, the scrubbing materials of the presentdisclosure typically have cementitious and/or pozzolanic properties. Asrecognized by those of skill in the art, the amount of water present ina system dictates the amount of cementitious phase formation, hence theextent of strengthening, hardening, and agglomeration. For example,concrete preferably minimizes the water content to enhance strength andhardness, for example, water to Portland cement ratios in concretepreferably range from less than 0.35 to about 0.40, with a minimumamount of 0.25 required to complete the hydration reactions of cementcompounds. A typical concrete composition is about 7 to 15% cement, 14to 21% water and the remainder aggregates. For stabilization of wastes,full development of strength and hardness is desirable to preventleaching of various metals. For such waste stabilization, it has beensuggested that the water to solid ratio should be about 0.125 forappropriate setting and hardening reaction of reactive silicates. Thus,in the presence of relatively high amounts of water, the materials haveless propensity to set, harden, and agglomerate. Hence, variousembodiments of the disclosure provide relatively high water content, toprevent hardening, setting, and agglomeration, so that the materials arecapable of circulating as a scrubbing material in a carbon dioxideabatement system.

In some embodiments, the scrubbing material handling system within thescrubber device may have agitation points. Further, certain embodimentsmay include centrifuges, filters, screens, and/or settling regions toremove any larger particles to prevent build-up of larger agglomeratedparticles in the scrubber material handling equipment and lines. In someembodiments, a plasticizing agent is employed to minimize potentialagglomeration and to increase flowability of the scrubbing material.Suitable plasticizing agents include sugar (sucrose), superplasticizersused in concrete applications (such as polymeric plasticizers likepolycarboxylate ethers, naphthalene and/or melamine based polymers andcopolymers), and diesel fuel. Plasticizing agents are well known in theart and a variety of suitable compounds can be used in the scrubbingmaterials of the disclosure, including those known or to be developed inthe art.

In certain embodiments, a carbon sequestration material slurry forscrubbing carbon dioxide from a carbon dioxide containing fluid streamconsists essentially of a first component comprising one or morematerials selected from the group consisting of: cement kiln dust, limekiln dust, sugar beet lime, clinker dust, quick lime, slaked lime, andmixtures thereof. In such embodiments, the slurry further consistsessentially of a second component comprising a slag having a source ofreactive silicates and water as well. In certain embodiments, the slagis a stainless steel slag. In other embodiments of the disclosure, thescrubbing material may consist essentially of a first componentcomprising cement kiln dust and a second component comprising a slaghaving a source of reactive silicates and water, such as stainless steelslag.

In certain embodiments, the scrubbing material slurry comprises a firstcomponent at between about 15 to about 50% by weight, the secondcomponent at about 15 to about 50% by weight, and water at about 15 toabout 50% by weight of the total scrubbing material composition.

In embodiments where the scrubbing material is in a slurry form, theslurry preferably comprises particles having an average maximum particlesize of less than or equal to about 500 μm and an average surface areaof greater than or equal to about 1000 cm²/g. In some embodiments, theparticles have an average surface area of greater than or equal to about4,000 cm²/g; optionally greater than or equal to about 7,000 cm²/g, andin some embodiments greater than 10,000 cm²/g. Further, the particles ofthe slurry have an average maximum particle size diameter of less thanor equal to about 300 μm in some embodiments, and less than or equal toabout 100 μm in other embodiments. Smaller particle sizes tend to havehigher surface areas, which promotes reaction of the active ingredients,minimizes settling effects of the particles from suspension andminimizes clogging of handling and processing equipment. In this regard,the suspended particles have desirable characteristics for reaction withthe carbon dioxide in the effluent stream and for transport andprocessing (preventing settling and the like). Such particle sizes andsurface areas may be achieved by selecting the first component andsecond component to have these desired properties or by furtherprocessing the materials by milling or grinding, for example, byadmixing the first and second components in a ball mill to reduceparticle size. The slurry may also be processed in a mixer, agitator,pug mill, or slurry mill to achieve sufficient mixing of the firstcomponent, second component, and water.

FIG. 1 depicts a process flow diagram of a carbon dioxide removal systemin accordance with one embodiment of the disclosure. A first component10, a second component 12, and water 14 are combined to form a freshscrubbing material 16. The fresh scrubbing material 16 may be stored ina tank prior to use in a reactor 20. The fresh scrubbing material 16 isintroduced into the reactor 20 and is contacted with an effluent stream22 containing carbon dioxide to scrub and remove the carbon dioxide. Thereactor 20 comprises a mixing zone 24, where the fresh scrubbingmaterial 16 and the effluent stream 22 are combined, preferably withturbulent flow. The scrubbing material 16 reacts with the carbon dioxideto form a product 26 collected within the reactor 20. The product 26comprises calcium carbonate and spent scrubbing material. The product 26exits the reactor 20 and enters a separator 28, where the calciumcarbonate product 30 is separated from spent scrubbing material 32.

As discussed above, it is believed that the active compounds arereactive silicates and calcium oxide. While not limiting as to thepresent teachings, it is believed that the scrubbing material undergoesthe following reaction mechanisms. The water and carbon dioxide formcarbonate anions in a basic pH solution. The carbonate anions react withcalcium ions in the presence of reactive silicates to form calciumcarbonate. The spent scrubbing material 16 comprises the reactivesilicates. The alkali metal ions provide desirable basicity to thesolution, which promotes reaction of the carbon dioxide with the calciumoxide and silicates, and further is believed to favor formation ofreactive silicate products in the spent scrubbing materials. The spentscrubbing material 32 still contains reactive silicates and desirablyhigh alkali metal ions, which help to maintain the pH. It is believedthat the carbonation reaction reduces the pH (to more neutralconditions) of the scrubbing material, thus the alkalinity of the firstcomponent is desirable.

In certain embodiments, the scrubbing system is continuous andregenerative. Thus, after the contacting in the mixing zone 24 of thereactor 20 the spent scrubbing composition 32 is separated from theproduct. The spent scrubbing material 32 is optionally returned to thefresh scrubbing material source 16. In this manner, the spent scrubbingmaterial 32 can be combined with fresh scrubbing material 16 prior tosubsequent contacting with the carbon dioxide containing fluid stream.Thus, a portion of the spent scrubbing material 32 can be recycled intothe fresh scrubbing material 16, desirably providing both reactivesilicates and alkalinity to promote a basic pH scrubbing materialslurry. The spent scrubbing material 32 can also be removed from thesystem for disposal 34.

In certain embodiments, the spent scrubbing material 32 and/or freshscrubbing material 16 are monitored to determine how much recycling oralternatively, purging of the scrubbing material (via disposal) isnecessary. For example, the spent scrubbing material 32 and/or themixture of spent and fresh scrubbing material can be monitored atrepresentative points 36 and 38 for an alkali ion content of the spentscrubbing material. If the alkali ion content is too low or too high,i.e., if the alkali metal ion content deviates from a predetermined setpoint, a portion of the spent scrubbing material is then removed. Forexample, if the concentration of alkali metal ions is too low, thedesired alkalinity may be too low for recycling. Further, if the alkalimetal ion content is too high, the spent scrubbing material 32 can bepurged. The predetermined amount can be used in a control system and canbe determined by empirical observation of the system and/or bycalculations modeling the system. Likewise, the pH of the spentscrubbing material 32 and/or a mixture of the spent scrubbing materialwith fresh scrubbing material can be monitored at representative 36 and38. If the pH exceeds a predetermined set point, a portion of the spentscrubbing material 32 is removed via disposal 34. The ranges ofpredetermined pH can be ascertained by empirical observation and/orcalculation. As described previously, in certain aspects, the scrubbingmaterial contacting the carbon dioxide has a basic pH of greater than orequal to about 7, preferably greater than or equal to about 9, and insome circumstances greater than or equal to about 11.

As described above, it is preferable that the scrubbing material 16contacts fluid stream 22 in a turbulent mixing zone 24 of the reactor20. In embodiments where the scrubbing material is a slurry, the highenergy slurry stream contacts the gas stream and effects mass transfer.The mixing zone 24 preferably provides a high surface area to achievesufficient mass transfer. In typical manufacturing facilities, effluentor exhaust streams from various processes have flow rates ranging fromabout 10,000 actual ft³/min (acfm) (about 285 m³/min) to about 1,000,000acfm (about 28,000 m³/min). However, as appreciated by those of skill inthe art, such flow rates vary based on the capacity of the facility andthe type of process, and are difficult to generalize. For example, kilnexhaust from a typical cement manufacturing facility is usually betweenabout 100,000 acfm (2,800 m³/min) to about 400,000 acfm (about 11,000m³/min) and typical boiler exhaust flow rates can range from about100,000 (2,800 m³/min) to about 600,000 acfm (17,000 m³/min). Thus, incertain embodiments, the reactor 20 is capable of processing typicalindustrial exhaust gas flow rates.

In certain embodiments, the contacting occurs at ambient pressureconditions. In various embodiments, the contacting of the scrubbingmaterial 16 and the effluent fluid stream 22 occurs in an environment atless than or equal to about 100° C. (212° C.) at ambient pressure, toprevent evaporation of the water in the slurry. In this regard, theeffluent stream 22 may need to be cooled, for example by a heatexchanger shown as 40 in FIG. 1, prior to contacting the scrubbingmaterial or the pressure of the system may need to be increased toprevent undesirable evaporation of the water. In some embodiments, thecontacting occurs in an environment of less than or equal to about 75°C. (approximately 170° F.); optionally less than or equal to about 40°C. (approximately 100° F.). In some embodiments, the contacting of thescrubbing material with the fluid stream occurs at ambient pressure andambient temperature conditions. Such embodiments may require cooling ofthe effluent stream prior to contact, as well known to those of skill inthe art and discussed above. Thus, the treated effluent 44 exits thereactor 20 having a reduced amount of carbon dioxide as compared to aninitial amount of carbon dioxide present in the untreated effluentstream 22. In certain aspects, the removal efficiency of the reactor 20is greater than 20%, optionally greater than 30%. In certain aspects,the removal efficiency is optimized to be greater than 50%; optionallygreater than 75%; optionally greater than 90%, and in some embodimentsgreater than 95%.

After the reaction of carbon dioxide in the effluent stream 22 with thescrubbing material 16, a product 26 comprising calcium carbonate andspent scrubbing material is generated. While some water may be lostduring the contacting and reaction, a large portion of water will remainin the product 26. In some embodiments, this product 26 may be agitatedto prevent agglomeration and/or hardening of the silicate materials. Thecalcium carbonate can then be processed via a separator 28 from thespent scrubbing material, for example by filtration. In certainembodiments, the calcium carbonate 30 has a beneficial reuse and can beemployed as a raw material in another process such that it is recycled.In some embodiments, the water content of a separated calcium carbonateproduct 30 may be too high. The calcium carbonate product may beseparated from the water to achieve desirable moisture content dependingon the end use. For example, such separation of the calcium carbonatecan be achieved by evaporation, separation, and/or by filtration (notshown in FIG. 1). Thus, suitable equipment may include heaters,centrifuges, screen filters, filter presses, rotary disk filters, vacuumfilters, and the like, as are well known in the art. When the spentscrubbing material 32 is separated in the separator 28, it may beprepared for disposal 34 or may be recycled by reintroducing it to freshscrubbing material 16. For such recycling, it may be desirable toagitate the mixture periodically during transport (non-laminar flow) andfurther to add water to reduce viscosity and enhance pumping (not shownin FIG. 1).

In some embodiments, the contacting of the scrubbing material occurs ina fluidized bed reactor, a slurry bed reactor, a venturi scrubber, aspray tower scrubber, a packed scrubber reactor, a continuously stirredtank reactor (CSTR), and/or any combinations thereof. In certainembodiments using a viscous scrubbing material slurry, the contactingoccurs in a slurry bed reactor, a spray tower scrubber and/or a CSTR. Inother embodiments, particularly where the scrubber material comprisessemi-dry particles, a fluidized bed reactor or a venture scrubber can beused. The listing of the above reactors is non-limiting, as othersuitable reactors well known in the art are contemplated by the presentdisclosure.

Fluidized bed reactors suspend solid particles on upward-blowing jets ofgas during the reaction process and are well known in the art. Forexample, atmospheric fluidized beds use a sorbent to capture sulfurgenerated by fossil fuel combustion. In certain aspects, fluid shouldflow upward and have sufficient fluid velocity to lift the particles viafriction forces. In this manner, a turbulent mixing of solids and gasesis achieved. In certain aspects of the disclosure, the effluent streammay comprise sufficient water (or the water can be added prior to thereactor in the effluent stream or in the scrubbing material, ifnecessary) to enable reaction with a semi-dry scrubbing material in afluidized bed reactor.

Wet scrubbing generally uses a high energy liquid stream to contact thegas stream and affect mass transfer. In continuously stirred tankreactors (CSTR) one or more fluid reagents are introduced into a tankreactor equipped with one or more impeller(s). The impeller stirs thereagents to ensure proper mixing. Effluent is continuously removed fromthe tank. CSTRs often contain baffles and multiple inlets and/oreffluent removal points to provide homogeneity in the mixing. Further,the effluent fluid/gas can be injected into the CSTR at numerouslocations within the reactor to enhance mixing and the gas/liquid/solidinterfaces.

Wet scrubber reactors are often used in flue gas desulfurizationprocesses. There are several main kinds of wet scrubbers, including aventuri scrubber, a packed tower scrubber, and a spray tower scrubber. Aventuri scrubber is a converging/diverging section of duct. Theconverging section accelerates the fluid stream to a high velocity. Whenthe slurry stream is injected at the throat or point of maximumvelocity, the turbulence caused by the high gas velocity atomizes theliquid into small particles and/or droplets, which creates the surfacearea necessary for mass transfer to take place. The higher the pressuredrop in the venturi, the smaller the atomized particles and the higherthe surface area.

A packed scrubber reactor consists of a tower with small objectsdisposed therein. These objects can be in the shape of saddles, rings orspecialized shapes that are designed to maximize contact area betweenthe exhaust gas and liquid. Packed towers typically operate at muchlower pressure drops than a venturi scrubber and typically providehigher pollutant removal efficiency. In certain aspects, theliquid/slurry has a low viscosity when used in such a reactor.

Most wet scrubbers are designed as a spray tower. A spray tower scrubberreactor has a relatively simple design, which consists of a tower withspray nozzles, which generate the droplets for surface contact. A spraytower is one particularly suitable reactor for using a slurry scrubber,as such towers generally avoid material plugging.

The tower is typically designed so that, at maximum load, the averagesuperficial gas velocity will not exceed the design gas velocity. Formost spray towers, the average gas velocity varies from about 8 to 13ft/sec. (2.4 to 4 m/sec) based upon scrubber outlet conditions; however,the present disclosure is not limited to any particular velocities. Theeffluent/flue gas enters the absorber reactor from a side fluid inlet.The design of the tower is influenced by the scrubbing material, thedesired CO₂ removal level, a tradeoff between fan power andrecirculation slurry pump power, as well as several other factors wellknown to those of skill in the art. Spray nozzles are conventionallyused in wet scrubbers, and such nozzles assist with controlling themixing of scrubbing material slurry with the effluent gas. The operatingpressures typically vary between about 5 and 20 psi (34 and 138 kPa),although the disclosure is not limited to such exemplary pressures.Spray nozzles without internal obstructions are favored to minimizeplugging by trapped debris. A large tank at the bottom of the spraytower/reaction chamber is usually referred to as a reaction tank or therecirculation tank. The volume of this tank permits several chemical andphysical processes to approach completion. Gas-liquid-solid contactingin the towers permits high efficiency for pollutant removal andmaximization of reagent utilization. The gas follows the reactionchamber walls to the rear end of the absorber exits at the rear of theabsorber.

As shown in FIG. 2, in certain embodiments, a carbon dioxide emissionabatement system comprises a scrubber tower reactor 100 that comprises areaction chamber 102. The reaction chamber 102 is in fluid communicationwith a fluid inlet/inlet passage 104, here shown as a down corner duct.The fluid inlet 104 permits ingress of an effluent fluid stream into thereaction chamber 102. The effluent fluid stream 106 preferably isgenerated upstream in a furnace, an incinerator, a boiler, or a kiln,and comprises carbon dioxide. A source of slurry 108 comprises a slurry110 having a first component comprising a source of calcium oxide and asource of alkali metal ions; a second component comprising a slag havinga source of reactive silicates; and water. The source of slurry 108 isin fluid communication with a slurry inlet 112 a disposed in thereaction chamber 102 that feeds slurry 108 to the reaction chamber 102.It should be noted that in alternate embodiments, the slurry 110 can beintroduced in the inlet passage 104 with the effluent stream 106, forexample, at an alternate slurry inlet 112 b. Further, in certainembodiments, the slurry 110 can be introduced at both slurry inlets 112a and 112 b. The source of slurry 108 generally comprises a storage tank(not shown) and a pumping system 113.

The reaction chamber 102 also comprises a mixing zone 114 disposed inthe reaction chamber 102. The mixing zone 114 is designed to turbulentlymix the effluent fluid stream 106 and the slurry 110. The mixing zone114 may further contain additional means for effecting turbulence, forexample baffles or chevron plates 116 (for simplicity only shown in asmall portion of the mixing zone, but which can extend throughout themixing zone 114) for enhancing the opportunity for interface between theeffluent gas 106 and the slurry 110 within the reactor 100. Further, thereaction chamber 102 is sized, or has a volume sufficient to provide aresidence time, that enables treatment of the effluent stream to reducean amount of carbon dioxide by a suitable amount, which is at leastabout 30% in a preferred embodiment. A residence time generally refersto

${T = \frac{{reactor}\mspace{14mu}{volume}}{{gas}\mspace{14mu}{flow}\mspace{14mu}{rate}}},$indicating a mean time that a molecule is within a reactor 100. As such,in accordance with certain aspects of the disclosure, the reactorchamber 102 is sized to have a volume that permits the effluent fluid106 to have a sufficient residence time to react with the scrubbingmaterial slurry 110. As appreciated by those of skill in the art, suchvolumes can be determined by the flow rate of effluent fluid to betreated.

The reactor system 100 further comprises a fluid outlet passage 118 influid communication with the reaction chamber 102 to permit egress ofthe treated effluent stream 120 from the reaction chamber 102. A largereservoir 124 at the bottom 126 of the reaction chamber 102 is usuallyreferred to as a reaction tank or the recirculation tank. This reservoir124 is sized to permit the desired carbon sequestration reactions toapproach completion without allowing setting or hardening of the spentslurry/product collected there. While not shown, the reservoir 124optionally comprises agitation equipment, such as agitation screens orpumps, for example, that furthers the objective of preventing setting ofthe spent scrubbing material. A slurry outlet/removal passage 122 is influid communication with the reactor chamber 102 for removing spentslurry and/or a calcium carbonate product 128. While not shown in FIG.2, the spent slurry solution can be separated from calcium carbonate andthen recirculated into the slurry source 108.

FIG. 3 depicts one embodiment of a carbon dioxide removal system muchthe same as that shown in FIG. 1, but comprising one or more airpollution control devices 50 (APCDs) that further treat the effluentstream 44 after it has exited the reactor 20. As appreciated by those ofskill in the art, the effluent stream comprises one or more additionalpollutants other than CO₂. For example, in addition to carbon dioxide,common air pollutants found in effluent streams from boilers, kilns,furnaces, and incinerators include carbon monoxide, hydrochloric acid,chlorofluorocarbons, nitrous oxides, sulfur oxides, particulate matter,volatile organic compounds, aerosol compounds, mercury, lead, ammonia,ozone, and mixtures and equivalents thereof. Thus, in some embodiments,the reactor 20 may serve to incidentally remove a portion of these otherpollutants, however, it is contemplated that additional APCDs 50 may berequired to reduce the one or more additional pollutants to acceptableconcentrations. Typical exemplary APCDs 50 include electrostaticprecipitators, baghouse filters, cyclones, activated carbon scrubbers,flue gas desulfurization scrubbers, thermal oxidizers, pressure swingadsorbers, selective catalytic reactors, selective non-catalyticreactors, and the like.

In certain embodiments, such as those shown in FIG. 4, the carbondioxide removal system further comprises one or more air pollutioncontrol devices 60 (APCDs) to pre-treat the effluent stream 22 prior toentering the reactor 20. Thus, any additional pollutants can be removedthat may cause adverse or undesirable reactions with the scrubbingmaterial or corrosion or damage to the equipment hardware.

In certain aspects, the present disclosure provides a method of reducingcarbon dioxide emissions from a cement manufacturing facility. Themethod comprises reacting cement manufacturing raw materials (containingsources of calcium, silicon, aluminum, and iron) in a kiln to produceclinker and an effluent stream comprising carbon dioxide. At least aportion of the effluent stream is contacted with a scrubbing materialsuch as those described in previous embodiments above. A product isgenerated that comprises calcium carbonate and a spent scrubbingcomposition. Any of the processes of the embodiments described above maybe useful for the present embodiments. For example, prior to thecontacting the effluent with scrubbing material, the effluent stream canbe processed in one or more air pollution control devices (APCDs) toremove one or more air pollutants. Limestone or calcium carbonate is aprimary raw material in the manufacture of both lime and cement. Incertain embodiments, the product comprising calcium carbonate isbeneficially re-used as a raw material to produce clinker and/or lime.Thus, in cement manufacturing, the generated calcium carbonate issubsequently combined with the raw materials to produce the clinker.

The spent scrubbing material can be recycled, as described previouslyabove. In some embodiments, the methods further comprise generatingcement kiln dust (CKD) during the reaction of the raw materials. Thescrubbing material can comprise at least a portion of the generatedcement kiln dust (CKD). The CKD can be collected via a particulatematter APCD (e.g., baghouse or ESP) and then introduced into thescrubbing material. However, it is also contemplated that in certainembodiments, the effluent stream contacts the scrubbing material beforeentering a particulate matter control device, thus the CKD particles areentrained in the effluent stream and can supplement the scrubbingmaterial as a source of calcium ions and alkali metal ions. As describedabove, in certain preferred aspects, the first component comprisescement kiln dust (CKD) and the second component comprises stainlesssteel slag.

Some manufactured cement is designated as low alkali and as such, theraw materials for making the cement likewise must have relatively lowalkali content. If the alkali metal ions partition into the calciumcarbonate product, it may be necessary to reduce the concentration ofalkali ions in the calcium carbonate product to promote partitioning tothe spent scrubbing product. In this manner, the spent scrubbingmaterial and/or calcium carbonate product can be monitored for alkaliion content to prevent unwanted alkali build-up in the kiln or clinkerproduct.

In other embodiments of the disclosure, a method for reducing carbondioxide emissions from a cement and/or lime manufacturing facility isprovided. The scrubbing material is contacted with at least a portion ofan effluent stream comprising carbon dioxide. The effluent stream isgenerated in a kiln. The scrubbing material comprises a first component,a second component distinct from the first component, and water, as inany of the embodiments previously described. The method furthercomprises generating a product comprising calcium carbonate and a spentscrubbing material. The calcium carbonate product is then re-used as araw material in the kiln. In some embodiments, the reacting of the rawmaterials further comprises generating cement kiln dust (CKD) or limekiln dust (LKD) and the scrubbing material comprises at least a portionof the generated cement kiln dust (CKD) or lime kiln dust (LKD).

The present disclosure further provides embodiments to reduce carbondioxide emissions from an iron and/or steel manufacturing facility. Themethod comprises contacting a scrubbing material with at least a portionof an effluent stream comprising carbon dioxide that is generated in afurnace of an iron and/or steel manufacturing process. The furnace canbe any of those described above in the context of the slag sources, suchas a blast furnace (iron ore processing), an open hearth furnace (steelprocessing), a basic oxygen process furnace (steel processing), or anelectric arc furnace (steel processing). The scrubbing materialcomprises a first component, a second component distinct from the firstcomponent, and water, as where described above. A product comprisingcalcium carbonate is generated that is capable of reuse as a rawmaterial in an industrial process. In certain embodiments, the secondcomponent comprises a slag generated in the iron and/or steelmanufacturing process. Further the calcium carbonate product can berecycled and used as a flux material in the iron and/or steelmanufacturing process. In other embodiments, the calcium carbonate canbe used as a raw material in any industry that employs calcium carbonateas a raw material, such as in cement and lime manufacturing.

In yet other embodiments, methods of reducing carbon dioxide emissionsfrom a hydrocarbon combustion source, such as a power plant boiler or anincinerator, are provided. A hydrocarbon combustion source comprises allstationary point sources that combust hydrocarbons that form carbondioxide, including those facilities that burn fossil-fuels (e.g., coal,methane), synthetic fuels (e.g., petroleum coke, syngas, ethanol), orany other variety of hydrocarbons. The process comprises contacting ascrubbing material with at least a portion of an effluent streamcomprising carbon dioxide that is generated by combustion of afossil-fuel. The scrubbing material is any of those described above. Aproduct comprising calcium carbonate that is capable of reuse as a rawmaterial in an industrial process is thus generated.

In various embodiments, the present disclosure provides methods ofrecycling industrial byproducts which would otherwise be stockpiled,land-filled, or discarded. For example, in certain embodiments, a methodof recycling industrial byproducts is provided. A carbon dioxidescrubbing material is formed by admixing a first manufactured componentwith a second manufactured component. The first component comprises asource of calcium oxide and a source of alkali metal ions. The secondcomponent comprises a slag having one or more reactive silicatecompounds. An effluent stream generated in an industrial processcomprising carbon dioxide is then contacted with the scrubbing material.A product comprising calcium carbonate is generated that is capable ofbeneficial reuse such as in an industrial process. In some embodiments,after the contacting and after the generating, the scrubbing material isspent and at least a portion of the spent scrubbing material is admixedwith the fresh first manufactured component and the fresh secondmanufactured component.

In this manner, the methods and scrubbing materials of the disclosurefurther sustainable development initiatives, which include balancing theneed for current growth and development against the need to protect thenatural and manmade environment for future generations. Further, themethods and systems of the disclosure provide reduced carbon dioxideemissions for various stationary point sources, which in addition toreducing greenhouse gas emissions, provides the ability for such pointsources to comply with various regulations, to receive an economic andcommercial benefit through carbon dioxide emission credit tradingprograms, and to reduce potential corrosion and inefficiencies attendantwith the presence of carbon dioxide in effluent streams.

1. A method of removing carbon dioxide from an effluent streamcomprising carbon dioxide, the method comprising: reducing an amount ofcarbon dioxide in the effluent stream by contacting the effluent streamwith a scrubbing material comprising: (i) a first component comprising asource of calcium oxide and a source of alkali metal ions and (ii) asecond component comprising one or more reactive silicate compounds,wherein the first component is distinct from the second component,wherein the contacting occurs in the presence of water and the alkalimetal ions of the first component contribute to increasing a pH of thescrubbing material to about 9 or higher to increase the rate of reactionof the carbon dioxide with the scrubbing material, wherein thecontacting reduces a total amount of the carbon dioxide to less than orequal to about 50% of an initial amount of the carbon dioxide prior tothe contacting.
 2. The method according to claim 1, wherein after thecontacting, the amount of carbon dioxide is less than or equal to about75% of an initial amount of carbon dioxide prior to the contacting. 3.The method according to claim 1, wherein the effluent stream isgenerated by an industrial process and further comprises one or moreadditional air pollutants selected from the group consisting of: carbonmonoxide, chlorofluorocarbons, hydrochloric acid, nitrous oxides, sulfuroxides, particulate matter, volatile organic compounds, aerosolcompounds, mercury, lead, ammonia, and ozone, wherein the contactingwith the scrubbing material also reduces an amount of at least one ofthe one or more additional air pollutants in the effluent stream.
 4. Themethod according to claim 3, wherein the one or more additional airpollutants is selected from the group consisting of: carbon monoxide,hydrochloric acid, nitrous oxides, sulfur oxides, particulate matter,volatile organic compounds, aerosol compounds, mercury, lead, ammonia,and ozone.
 5. The method according to claim 1, wherein the firstcomponent comprises a material selected from the group consisting of:cement kiln dust (CKD), lime kiln dust (LKD), sugar beet lime (SBL),clinker dust, slaked lime, quick lime, and combinations thereof, and thesecond component comprises a material selected from the group consistingof: blast furnace slag, steel slag, and combinations thereof, and aratio of the first component to the second component in the scrubbingmaterial is about 10:1 to about 1:10.
 6. The method according to claim1, wherein the first component comprises cement kiln dust (CKD) and thesecond component comprises a stainless steel slag.
 7. The methodaccording to claim 1, wherein the scrubbing material further compriseswater, wherein the scrubbing material comprises about 15% by weight toabout 50% by weight of the first component, about 15% by weight to about50% by weight of the second component, and about 15% by weight to about50% by weight of water.
 8. The method according to claim 1, wherein thecontacting is a continuous process and the effluent stream is generatedby an industrial process that has a flow rate of greater than or equalto about 10,000 actual ft³/min (acfm) to less than or equal to about1,000,000 actual ft³/min (acfm) and the contacting occurs in a reactorselected from the group consisting of: a fluidized bed reactor, a bedreactor, a venturi scrubber, a spray tower scrubber, a packed scrubberreactor, a continuously stirred tank reactor, and combinations thereof.9. The method according to claim 1, wherein the first componentcomprises: calcium oxide (CaO) at about 30% to about 45% by weight;silica (SiO₂) at about 10% to about 20% by weight; alumina (Al₂O₃) atabout 2% to about 7% by weight; iron oxide (Fe₂O₃) at about 1% to about3% by weight; magnesium oxide (MgO) at about 0.5% to about 3% by weight;sulfate (SO₃) at about 1% to about 15% by weight; sodium oxide (Na₂O) atabout 0.1% to about 1% by weight; and potassium oxide (K₂O) at about0.1% to about 15% by weight, and the second component comprises: silica(SiO₂) at about 10% to about 35% by weight; calcium oxide (CaO) at about35% to about 55% by weight; magnesium oxide (MgO) at about 3% to about10% by weight; iron oxide (FeO) at about 0.1% to about 40% by weight;and alumina (Al₂O₃) at about 0.1% to about 10% by weight.
 10. A methodof removing carbon dioxide from an effluent stream comprising carbondioxide, the method comprising: reducing an amount of carbon dioxide inthe effluent stream by contacting the effluent stream with a scrubbingmaterial comprising (i) a first component comprising a source of calciumoxide and a source of alkali metal ions and (ii) a second componentcomprising one or more reactive silicate compounds, wherein the firstcomponent is distinct from the second component, a ratio of the firstcomponent to the second component in the scrubbing material is about10:1 to about 1:10 and a molar ratio of calcium (Ca) to silicon (Si) inthe scrubbing material is about 1:1 to about 10:1, wherein thecontacting occurs in the presence of water, and the alkali metal ions ofthe first component contribute to increasing a pH of the scrubbingmaterial to about 9 or higher to increase the rate of reaction of thecarbon dioxide with the scrubbing material, and the contacting reduces atotal amount of the carbon dioxide to less than or equal to about 50% ofan initial amount of the carbon dioxide prior to the contacting.
 11. Themethod according to claim 10, wherein after the contacting, the amountof carbon dioxide is less than or equal to about 75% of an initialamount of carbon dioxide prior to the contacting.
 12. The methodaccording to claim 10, wherein the effluent stream is generated by anindustrial process and further comprises one or more additional airpollutants selected from the group consisting of: carbon monoxide,chlorofluorocarbons, hydrochloric acid, nitrous oxides, sulfur oxides,particulate matter, volatile organic compounds, aerosol compounds,mercury, lead, ammonia, and ozone, wherein the contacting with thescrubbing material also reduces an amount of at least one of the one ormore additional air pollutants in the effluent stream.
 13. The methodaccording to claim 12, wherein the one or more additional air pollutantsis selected from the group consisting of: carbon monoxide, hydrochloricacid, nitrous oxides, sulfur oxides, particulate matter, volatileorganic compounds, aerosol compounds, mercury, lead, ammonia, and ozone.14. The method according to claim 10, wherein the first componentcomprises a material selected from the group consisting of: cement kilndust (CKD), lime kiln dust (LKD), sugar beet lime (SBL), clinker dust,slaked lime, quick lime, and combinations thereof, and the secondcomponent comprises a material selected from the group consisting of:air cooled blast furnace slag, granulated blast furnace slag, groundgranulated blast furnace slag, expanded and/or pelletized blast furnaceslag, basic oxygen furnace steel slag, open hearth furnace steel slag,electric arc furnace steel slag, and combinations thereof, and a ratioof the first component to the second component in the scrubbing materialis about 10:1 to about 1:10.
 15. The method according to claim 10,wherein the first component comprises cement kiln dust (CKD) and thesecond component comprises a stainless steel slag.
 16. The methodaccording to claim 10, wherein the scrubbing material further compriseswater, wherein the scrubbing material comprises about 15% by weight toabout 50% by weight of the first component, about 15% by weight to about50% by weight of the second component, and about 15% by weight to about50% by weight of water.
 17. A method of removing carbon dioxide from aneffluent stream generated by an industrial process comprising carbondioxide, the method comprising: reducing an amount of carbon dioxide inthe effluent stream generated by the industrial process by contactingthe effluent stream with a scrubbing material comprising (i) a firstcomponent selected from the group consisting of: cement kiln dust (CKD),lime kiln dust (LKD), sugar beet lime (SBL), clinker dust, slaked lime,quick lime, and combinations thereof and (ii) a second componentcomprising a material selected from the group consisting of: blastfurnace slag, steel slag, and combinations thereof, wherein thecontacting occurs in the presence of water, wherein the alkali metalions of the first component contribute to increasing a pH of thescrubbing material to about 9 or higher to increase the rate of reactionof the carbon dioxide with the scrubbing material, wherein thecontacting reduces a total amount of the carbon dioxide to less than orequal to about 50% of an initial amount of the carbon dioxide prior tothe contacting.
 18. The method according to claim 17, wherein thescrubbing material further comprises water, wherein the scrubbingmaterial comprises about 15% by weight to about 50% by weight of thefirst component, about 15% by weight to about 50% by weight of thesecond component, and about 15% by weight to about 50% by weight ofwater.
 19. The method according to claim 17, wherein the first componentcomprises cement kiln dust (CKD) and the second component comprises astainless steel slag.
 20. The method according to claim 17, wherein thefirst component comprises: calcium oxide (CaO) at about 30% to about 45%by weight; silica (SiO₂) at about 10% to about 20% by weight; alumina(Al₂O₃) at about 2% to about 7% by weight; iron oxide (Fe₂O₃) at about1% to about 3% by weight; magnesium oxide (MgO) at about 0.5% to about3% by weight; sulfate (SO₃) at about 1% to about 15% by weight; sodiumoxide (Na₂O) at about 0.1% to about 1% by weight; and potassium oxide(K₂O) at about 0.1% to about 15% by weight, and the second componentcomprises: silica (SiO₂) at about 10% to about 35% by weight; calciumoxide (CaO) at about 35% to about 55% by weight; magnesium oxide (MgO)at about 3% to about 10% by weight; iron oxide (FeO) at about 0.1% toabout 40% by weight; and alumina (Al₂O₃) at about 0.1% to about 10% byweight.